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close this bookBoiling Point No. 19 - August 1989 (ITDG, 1989, 36 p.)
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Pakistan Villages - Improved Stoves

Summary of results of a field study of the traditional mud stove used in North-West Pakistan - July 1988 by Hilda V Krosigk

Within the context of stove development and dissemination of the Domestic Energy Saving Project (DESP) funded by the German Agency for Technical Cooperation (GTZ) a field study was carried out on the traditional mud stove used in the Swali District of NW Pakistan.

A fuel survey completed 6 months earlier had made evident that there was a severe fuel scarcity in the area concerned. As the women had emphasized that any solution to fuel problems should not cost money, it was not likely that dissemination of an improved metal stove already developed by the project and disseminated in Afghan refugee camps would meet the women's demands.

Through the field study it was to be found out whether, by means of simple improvements of the traditional mud stove, efficiency could be increased and fuel consumption reduced. Two hundred stoves in 60 households of 9 villages were inspected within a period of 3 weeks in July 1988.


Fig 1 - Traditional, Permanent Mudstoves

Main Results

In the villages concerned, a traditional, fixed, mud stove is used, built from a strong, long lasting, sun dried mud mixed by the women themselves.

-It works economically on different sizes and kinds of low grade fuel; mainly bushes and small tree branches supplemented by dry grass, leaves and any kind of agricultural residue available. Firewood has long been a fuel of secondary importance.

- Loading of the stove with fuels of different shapes and sizes gives no problem.

- The fire is well protected from wind and rain.

- The design accommodates small and large sizes of pots.

- The building material is free from cost and everywhere available in the province.

- The women build the stove themselves and decide how many stoves they need and where to place them.

- The stoves are generally well built and maintained.

Description of Design


Fig 2 - Fixed, Mud Stoves

Each household has a variety of permanent stoves built in different shapes and sizes with 1,2 or 3 fireplaces in one stove unit. Most have 3 or 4 stoves with 8-10 fireplaces. The basic design of the firebox is constant. From the top view it has the shape of a horseshoe. At the back a protuding piece of stone or mud slants down to the bottom, decreasing the size of the firebox (back to front) thus allowing smaller pots (12-18cm dia) to be used. The smaller the pot, the deeper it sits into the firebox and the closer it is to the hearth. The two curves at the back provide outlets for hot gases.


Fig 3 - Stove For Lab Testing,

Big pots (26-40cm) always sit on the pot supports on the top of the stove but are not often used.

Firebox height

The firebox and consequently the fuel entrance become gradually smaller towards the bottom. The overall height of different stoves varies considerably. While the majority of those measured had a firebox height of 14-18 cm which is close to the optimum height for a woodstove ( 16cm), 36%C had a height of 19-24 cm. The reason for this is easily understood when one watches the way cooking is done with different fuels.

Ash from previous cooking is used to adapt the effective firebox height to the amount, size and type of fuel used. When necessary, ash is removed from or added to the hearth to get the firebox volume needed to start/reload the stove and to give the optimum fire bed to pot bottom height. With the variety of fuels used and this simple means of arranging the correct critical height, it is reasonable to build stoves with a firebox as sleep as 25cm and a "diameter" reducing from 22cm at the top to 12cm at the bottom.

Fuel Entrance

The average entrance is 17 cm wide with its height depending on the height of the stove. The entrance is not closed at the top which has a negative effect on the efficiency as cold air is drawn directly under the pot. However, it is easy to make and maintain and easier for the cook to watch the fire.


Fig 4- Portable Mud Stoves

In about one third of the households visited in July 198X a portable mud stove for small and medium sized pots was used in addition to the fixed stoves, some frequently, some only occasionally. They are built by the women in different shapes. Depending on the quality of the mud and how well they are made, the walls (not more than 6mm thick) break easily and have to be repaired frequently.

In many cases they are carelessly built. The pot supports are 1-3cm high, the fuel entrance is 14-20cm wide and efficiency depends on the condition and quality of the stove. They are moved around the compound to avoid cooking in the sun but are not meant to replace permanent stoves which all families have.

Fuels

The majority of households do not spend money on buying fuel. Men and children (mainly boys) daily spend long hours collecting fuel whilst looking after cattle etc. In 1988 only 10 out of 60 households visited bought fuel. Men and women interviewed considered that the fuel situation "has always been the same", no worse than in the days of their grandparents. They would not think of asking for support in the field of fuel provision and use. Nevertheless the ecological situation and the domestic fuel situation are threatening.

The women appreciate their own stoves; no other designs are known to them. Their standards of comparison are the gas or kerosene cookers used in the town. Their priority problems are:
- health care
- jobs for their husbands
- money to buy land, animals or a tractor - proper roads
- education for their children

Men are aware of a growing scarcity of fuel but do not regard it as a problem of high priority. Their answers were:
- you people will help us
- we have to do something about it
- but what? - goodness knows

Calorific Values of Fuels Used

FUEL

av.CAL

av.CAL


Values

Value %

firewood

19,000 kj/kg

100

bushes

14,000 kj/kg

74

s. cane

12,000kj/kg

64

c. dung

10,000 kj/kg

53

Cooking Performance of Fuels

FUEL

PHU(%)*

SSC (kg)**

f.wood + dung

24

0.122

s.cane+dung

22.5

0.172

wood only

18.3

0.120

bushes + dung

17.8

0.200

* PHU - Percentage Heat Utilized
** SSC - Specific Standard Consumption

One or 2 pieces of firewood develop enough heat to make dung burn easily with little smoke. In combination with fuels of lower heat value, ea. bushes, dung tends to smoulder, gases develop without burning as temperatures rise slowly, efficiency drops.

Bagasse burns fast and needs more attention unless combined with dung or wood. Bushes and brushwood are easy to feed into the stove, burn away quickly and so need constant attention unless mixed with firewood or dung.

The lower the calorific value of biomass fuels, the more weight and bulk is needed for the same heat energy powered by fuel of a higher calorific value.

Fuels such as bagasse or brushwood with high buy to weight ratios need more frequent feeding and attention for safety and are more difficult to transport. Compared to firewood, the use of low grade fuels not only increases the work of the cool it increases by up to to 40% the work of the men and children collecting and carrying the fuel home However, the point made at the beginning of the article must be kept in mind: "fuelwood has become a fuel of secondary importance".

Fuel Weights

Fuel

Weight

% weight increase


kg

on wood

firewood

0.405

-

bushes/dung

0.660

40%

s.cane/dung

0.560

29%

dung/f.wood

0.560

15%

Conclusion

The author of the study came to the conclusion that it was not advisable to put any effort into improving the traditional fixed stove design. Under the circumstances prevailing in the villages it would be very difficult, if not impossible, to develop and disseminate a stove design better than the one developed by the women themselves which meets complex demands under extremely difficult living conditions.

Note - Details of the test procedures and data obtained arc available from ITDG.